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    <script>
        function getsum(num1, num2) {
            console.log(num1 + num2);
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        //函数形参实参个数匹配问题
        getsum(1, 2);
        //实参比形参多，NaN
        getsum(1, 2, 3);
        //实参比形参少.NaN
        getsum(1);
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